Thanks for the note about Edison's assistant William Hammer. My statement was based on the description in Edison's 1884 U.S. Patent 00,307,031, which shows that Edison at least somewhat understood the rectifying effect when he wrote the description. Of course, he would have learned that from Hammer.

Edison states that "a portion of the current will, when the lamp is in operation, pass through the shunt-circuit thus formed {the diode plate circuit}, which shunt includes a portion of the vacuous space within the lamp", without mentioning the yet-to-be-discovered electron.

en.wikipedia.org/wiki/Thermionic_emission states that the Edmond Becquerel discovered the effect in 1853, and that Frederick Guthrie discovered the same effect in air in 1873.

en.wikipedia.org/wiki/J._J._Thomson states that Thomson discovered the electron in 1897, and has a description of his experiments with cathode rays.

Edison did invent the vacuum tube diode, and knew it, but had no use for it!

Here are four key U.S. patents on the early vacuum tube:

00,307,031 issued 1884, Thomas Edison, "vacuous" diode used as voltmeter (plate current depended on filament voltage). Edison was aware of the polarity-sensitive property of his diode, but worked with direct current only, so had no use for a rectifier.

00,879,532 issued 1908, Lee DeForest, gassy triode detector for radio. DeForest specified that a "conducting gaseous medium" was necessary for operation. DeForest used a capacitor in series with the grid to block DC grid current, and let the gas determine the grid voltage.

01,558,436 issued 1925, Irving Langmuir of General Electric, vacuum triode detector and oscillator for radio. Langmuir patented the vacuum (so has a patent on the absence of gas). Langmuir filed in 1913, but issuance of this patent was delayed until eight months after DeForest's patent expired, so triode vacuum tubes were under patent until 1942.

Harold D. Arnold of AT&T independently invented the triode vacuum tube for telephone use, but I do not have his patent number.

Remember that a major purpose of the U.S. Patent Office is the creation of expired utility patents as an open record of technological how-to. The limited-term patent monopoly is merely a means to this end.

Would that be the same Edison that didn't create the world's first incandescent bulb and who missed the chance to invent the vacuum tube 21 years before British electrical engineer and physicist John Ambrose Fleming created the vacuum tube diode?

@David: ....our parliament on TV often looks like an unsupervised kindergarten class...

You think you've got it bad... you should see what it's like over here in the USA these days... I'm scared to turn my TV on to discover the Disaster du Jour (we consider ourselves lucky if there's only one :-)